1. Field of the Invention
This invention concerns tank caps for fluid containers. Specifically, a tank cap is provided with tang elements for engagement with a tank filler neck. A plurality of tang elements are divided into two pairs. One pair of tang elements will make contact with the filler neck prior to engagement of the second set. Therefore, sequential engagement and disengagement will be possible assisting in cap and filler neck alignment.
2. Description of the Prior Art
Cap design for use in combination with fuel tanks of agricultural tractor vehicles generally incorporate a vented cap having a single tang member comprising a spring-like elongated member having first and second end portions. The filler neck to which the cap would be attached would be provided with internal inclined ramps progressing from the top of the filler neck inwardly a short distance for increasing the seal pressure of the cap on the filler neck as the cap is rotated or generally screwed into place on the filler neck.
The filler necks are sometimes abused in service by vehicle operators and servicing personnel. Occasionally, large fluid storage cans are used in the refilling operation and if a heavy storage can is rested on the edge of a large funnel inserted into the filler neck during filling the internal inclined ramps in the filler neck can be distorted and bent inwardly causing the inside diameter to be expanded. The conventional cap with its single tang member may not engage the inclined ramps (or cam surfaces) properly if the filler neck has been damaged in this manner. The cap could end up being uncentered resulting in one tang end portion missing the inclined ramp surface. Upon further rotation of the cap by the operator the tang end that missed the inclined ramp will, instead of riding up the inclined ramp, cut into the interior sidewall surface of the inclined ramp. In this partial engagement the cap will be held in place by tang spring force from only the properly engaged tang portion. The cap may appear to be tight due to the friction of the unengaged tang end that missed the inclined surface of the ramp and was forced to cut into the interior sidewall surface of the inclined ramp.
The cap presented in this specification incorporates a "self-threading" feature in its tang element design such that if one tang end misses the inclined ramp on an enlarged filler neck the shape of the end portions of the tangs will urge the tang ends in the direction of the inclined ramps causing the tang ends to climb onto the inclined ramp surfaces.
Multiple tang element caps are known in contemporary positively or negatively pressurized tanks systems. In these embodiments initial cap rotation in the removal mode releases a first set of tangs from engagement with the host inclined ramps allowing the seal between the cap and the filler neck to be compromised. Further cap rotation in the same direction is necessary for the disengagement of the second set of tangs and the ultimate removal of the cap. These caps are not similar to the caps of the instant invention as they are unvented caps while the cap set forth herein is a vented cap that would be inefficient on pressure or vacuum dependent storage tanks.